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# MessageFormat

`public class MessageFormat`
`` `` `extends UFormat` ``

java.lang.Object
↳ | java.text.Format
| ↳ | android.icu.text.UFormat
|  | ↳ | android.icu.text.MessageFormat

[icu enhancement] ICU's replacement for `MessageFormat`. Methods, fields, and other functionality specific to ICU are labeled '[icu]'.

MessageFormat prepares strings for display to users, with optional arguments (variables/placeholders). The arguments can occur in any order, which is necessary for translation into languages with different grammars.

A MessageFormat is constructed from a pattern string with arguments in {curly braces} which will be replaced by formatted values.

`MessageFormat` differs from the other `Format` classes in that you create a `MessageFormat` object with one of its constructors (not with a `getInstance` style factory method). Factory methods aren't necessary because `MessageFormat` itself doesn't implement locale-specific behavior. Any locale-specific behavior is defined by the pattern that you provide and the subformats used for inserted arguments.

Arguments can be named (using identifiers) or numbered (using small ASCII-digit integers). Some of the API methods work only with argument numbers and throw an exception if the pattern has named arguments (see `usesNamedArguments()`).

An argument might not specify any format type. In this case, a Number value is formatted with a default (for the locale) NumberFormat, a Date value is formatted with a default (for the locale) DateFormat, and for any other value its toString() value is used.

An argument might specify a "simple" type for which the specified Format object is created, cached and used.

An argument might have a "complex" type with nested MessageFormat sub-patterns. During formatting, one of these sub-messages is selected according to the argument value and recursively formatted.

After construction, a custom Format object can be set for a top-level argument, overriding the default formatting and parsing behavior for that argument. However, custom formatting can be achieved more simply by writing a typeless argument in the pattern string and supplying it with a preformatted string value.

When formatting, MessageFormat takes a collection of argument values and writes an output string. The argument values may be passed as an array (when the pattern contains only numbered arguments) or as a Map (which works for both named and numbered arguments).

Each argument is matched with one of the input values by array index or map key and formatted according to its pattern specification (or using a custom Format object if one was set). A numbered pattern argument is matched with a map key that contains that number as an ASCII-decimal-digit string (without leading zero).

### Patterns and Their Interpretation

`MessageFormat` uses patterns of the following form:

>      message = messageText (argument messageText)*
>      argument = noneArg | simpleArg | complexArg
>      complexArg = choiceArg | pluralArg | selectArg | selectordinalArg

>      noneArg = '{' argNameOrNumber '}'
>      simpleArg = '{' argNameOrNumber ',' argType [',' argStyle] '}'
>      choiceArg = '{' argNameOrNumber ',' "choice" ',' choiceStyle '}'
>      pluralArg = '{' argNameOrNumber ',' "plural" ',' pluralStyle '}'
>      selectArg = '{' argNameOrNumber ',' "select" ',' selectStyle '}'
>      selectordinalArg = '{' argNameOrNumber ',' "selectordinal" ',' pluralStyle '}'

>      choiceStyle: see ChoiceFormat
>      pluralStyle: see PluralFormat
>      selectStyle: see SelectFormat

>      argNameOrNumber = argName | argNumber
>      argName = [^[[:Pattern_Syntax:][:Pattern_White_Space:]]]+
>      argNumber = '0' | ('1'..'9' ('0'..'9')*)

>      argType = "number" | "date" | "time" | "spellout" | "ordinal" | "duration"
>      argStyle = "short" | "medium" | "long" | "full" | "integer" | "currency" | "percent" | argStyleText

- messageText can contain quoted literal strings including syntax characters. A quoted literal string begins with an ASCII apostrophe and a syntax character (usually a {curly brace}) and continues until the next single apostrophe. A double ASCII apostrohpe inside or outside of a quoted string represents one literal apostrophe.
- Quotable syntax characters are the {curly braces} in all messageText parts, plus the '#' sign in a messageText immediately inside a pluralStyle, and the '|' symbol in a messageText immediately inside a choiceStyle.
- See also `MessagePattern.ApostropheMode`
- In argStyleText, every single ASCII apostrophe begins and ends quoted literal text, and unquoted {curly braces} must occur in matched pairs.

Recommendation: Use the real apostrophe (single quote) character \\u2019 for human-readable text, and use the ASCII apostrophe (\\u0027 ' ) only in program syntax, like quoting in MessageFormat. See the annotations for U+0027 Apostrophe in The Unicode Standard.

The `choice` argument type is deprecated. Use `plural` arguments for proper plural selection, and `select` arguments for simple selection among a fixed set of choices.

The `argType` and `argStyle` values are used to create a `Format` instance for the format element. The following table shows how the values map to Format instances. Combinations not shown in the table are illegal. Any `argStyleText` must be a valid pattern string for the Format subclass used.

argType | argStyle | resulting Format object
--- | --- | ---
(none) | `null`
`number` | (none) | `NumberFormat.getInstance(getLocale())`
`integer` | `NumberFormat.getIntegerInstance(getLocale())`
`currency` | `NumberFormat.getCurrencyInstance(getLocale())`
`percent` | `NumberFormat.getPercentInstance(getLocale())`
argStyleText | `new DecimalFormat(argStyleText, new DecimalFormatSymbols(getLocale()))`
`date` | (none) | `DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())`
`short` | `DateFormat.getDateInstance(DateFormat.SHORT, getLocale())`
`medium` | `DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())`
`long` | `DateFormat.getDateInstance(DateFormat.LONG, getLocale())`
`full` | `DateFormat.getDateInstance(DateFormat.FULL, getLocale())`
argStyleText | `new SimpleDateFormat(argStyleText, getLocale())`
`time` | (none) | `DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale())`
`short` | `DateFormat.getTimeInstance(DateFormat.SHORT, getLocale())`
`medium` | `DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale())`
`long` | `DateFormat.getTimeInstance(DateFormat.LONG, getLocale())`
`full` | `DateFormat.getTimeInstance(DateFormat.FULL, getLocale())`
argStyleText | `new SimpleDateFormat(argStyleText, getLocale())`
`spellout` | argStyleText (optional) | `new RuleBasedNumberFormat(getLocale(), RuleBasedNumberFormat.SPELLOUT) .setDefaultRuleset(argStyleText);`
`ordinal` | argStyleText (optional) | `new RuleBasedNumberFormat(getLocale(), RuleBasedNumberFormat.ORDINAL) .setDefaultRuleset(argStyleText);`
`duration` | argStyleText (optional) | `new RuleBasedNumberFormat(getLocale(), RuleBasedNumberFormat.DURATION) .setDefaultRuleset(argStyleText);`

#### Differences from java.text.MessageFormat

The ICU MessageFormat supports both named and numbered arguments, while the JDK MessageFormat only supports numbered arguments. Named arguments make patterns more readable.

ICU implements a more user-friendly apostrophe quoting syntax. In message text, an apostrophe only begins quoting literal text if it immediately precedes a syntax character (mostly {curly braces}).
In the JDK MessageFormat, an apostrophe always begins quoting, which requires common text like "don't" and "aujourd'hui" to be written with doubled apostrophes like "don''t" and "aujourd''hui". For more details see `MessagePattern.ApostropheMode`.

ICU does not create a ChoiceFormat object for a choiceArg, pluralArg or selectArg but rather handles such arguments itself. The JDK MessageFormat does create and use a ChoiceFormat object (`new ChoiceFormat(argStyleText)`). The JDK does not support plural and select arguments at all.

#### Usage Information

Here are some examples of usage:

>      Object[] arguments = {
>          7,
>          new Date(System.currentTimeMillis()),
>          "a disturbance in the Force"
>      };

>      String result = MessageFormat.format(
>          "At {1,time} on {1,date}, there was {2} on planet {0,number,integer}.",
>          arguments);

>      output: At 12:30 PM on Jul 3, 2053, there was a disturbance
>                in the Force on planet 7.

Typically, the message format will come from resources, and the arguments will be dynamically set at runtime.

Example 2:

>      Object[] testArgs = { 3, "MyDisk" };

>      MessageFormat form = new MessageFormat(
>          "The disk \"{1}\" contains {0} file(s).");

>      System.out.println(form.format(testArgs));

>      // output, with different testArgs
>      output: The disk "MyDisk" contains 0 file(s).
>      output: The disk "MyDisk" contains 1 file(s).
>      output: The disk "MyDisk" contains 1,273 file(s).

For messages that include plural forms, you can use a plural argument:

     MessageFormat msgFmt = new MessageFormat(
         "{num_files, plural, " +
         "=0{There are no files on disk \"{disk_name}\".}" +
         "=1{There is one file on disk \"{disk_name}\".}" +
         "other{There are # files on disk \"{disk_name}\".}}",
         ULocale.ENGLISH);
     Map args = new HashMap();
     args.put("num_files", 0);
     args.put("disk_name", "MyDisk");
     System.out.println(msgFmt.format(args));
     args.put("num_files", 3);
     System.out.println(msgFmt.format(args));

     output:
     There are no files on disk "MyDisk".
     There are 3 files on "MyDisk".

See `PluralFormat` and `PluralRules` for details.

#### Synchronization

MessageFormats are not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.

See also:

- `Locale`
- `Format`
- `NumberFormat`
- `DecimalFormat`
- `ChoiceFormat`
- `PluralFormat`
- `SelectFormat`

## Summary

### Nested classes
`class` | `MessageFormat.Field` Defines constants that are used as attribute keys in the `AttributedCharacterIterator` returned from `MessageFormat.formatToCharacterIterator`.

### Public constructors
`MessageFormat(String pattern)` Constructs a MessageFormat for the default `FORMAT` locale and the specified pattern.
`MessageFormat(String pattern, Locale locale)` Constructs a MessageFormat for the specified locale and pattern.
`MessageFormat(String pattern, ULocale locale)` Constructs a MessageFormat for the specified locale and pattern.

### Public methods
`void` | `applyPattern(String pttrn)` Sets the pattern used by this message format.
`void` | `applyPattern(String pattern, MessagePattern.ApostropheMode aposMode)` [icu] Sets the ApostropheMode and the pattern used by this message format.
`static String` | `autoQuoteApostrophe(String pattern)` [icu] Converts an 'apostrophe-friendly' pattern into a standard pattern.
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`final StringBuffer` | `format(Object[] arguments, StringBuffer result, FieldPosition pos)` Formats an array of objects and appends the `MessageFormat`'s pattern, with arguments replaced by the formatted objects, to the provided `StringBuffer`.
`static String` | `format(String pattern, Map<String, Object> arguments)` Creates a MessageFormat with the given pattern and uses it to format the given arguments.
`final StringBuffer` | `format(Object arguments, StringBuffer result, FieldPosition pos)` Formats a map or array of objects and appends the `MessageFormat`'s pattern, with format elements replaced by the formatted objects, to the provided `StringBuffer`.
`final StringBuffer` | `format(Map<String, Object> arguments, StringBuffer result, FieldPosition pos)` Formats a map of objects and appends the `MessageFormat`'s pattern, with arguments replaced by the formatted objects, to the provided `StringBuffer`.
`static String` | `format(String pattern, Object... arguments)` Creates a MessageFormat with the given pattern and uses it to format the given arguments.
`AttributedCharacterIterator` | `formatToCharacterIterator(Object arguments)` Formats an array of objects and inserts them into the `MessageFormat`'s pattern, producing an `AttributedCharacterIterator`.
`MessagePattern.ApostropheMode` | `getApostropheMode()` [icu]
`Set<String>` | `getArgumentNames()` [icu] Returns the top-level argument names.
`Format` | `getFormatByArgumentName(String argumentName)` [icu] Returns the first top-level format associated with the given argument name.
`Format[]` | `getFormats()` Returns the Format objects used for the format elements in the previously set pattern string.
`Format[]` | `getFormatsByArgumentIndex()` Returns the Format objects used for the values passed into `format` methods or returned from `parse` methods.
`Locale` | `getLocale()` Returns the locale that's used when creating or comparing subformats.
`ULocale` | `getULocale()` [icu] Returns the locale that's used when creating argument Format objects.
`int` | `hashCode()` Returns a hash code value for the object.
`Object[]` | `parse(String source)` Parses text from the beginning of the given string to produce an object array.
`Object[]` | `parse(String source, ParsePosition pos)` Parses the string.
`Object` | `parseObject(String source, ParsePosition pos)` Parses text from a string to produce an object array or Map.
`Map<String, Object>` | `parseToMap(String source)` [icu] Parses text from the beginning of the given string to produce a map from argument to values.
`Map<String, Object>` | `parseToMap(String source, ParsePosition pos)` [icu] Parses the string, returning the results in a Map.
`void` | `setFormat(int formatElementIndex, Format newFormat)` Sets the Format object to use for the format element with the given format element index within the previously set pattern string.
`void` | `setFormatByArgumentIndex(int argumentIndex, Format newFormat)` Sets the Format object to use for the format elements within the previously set pattern string that use the given argument index.
`void` | `setFormatByArgumentName(String argumentName, Format newFormat)` [icu] Sets the Format object to use for the format elements within the previously set pattern string that use the given argument name.
`void` | `setFormats(Format[] newFormats)` Sets the Format objects to use for the format elements in the previously set pattern string.
`void` | `setFormatsByArgumentIndex(Format[] newFormats)` Sets the Format objects to use for the values passed into `format` methods or returned from `parse` methods.
`void` | `setFormatsByArgumentName(Map<String, Format> newFormats)` [icu] Sets the Format objects to use for the values passed into `format` methods or returned from `parse` methods.
`void` | `setLocale(ULocale locale)` Sets the locale to be used for creating argument Format objects.
`void` | `setLocale(Locale locale)` Sets the locale to be used for creating argument Format objects.
`String` | `toPattern()` Returns the applied pattern string.
`boolean` | `usesNamedArguments()` [icu] Returns true if this MessageFormat uses named arguments, and false otherwise.

### Inherited methods
From class `java.text.Format`
`Object` | `clone()` Creates and returns a copy of this object.
`final String` | `format(Object obj)` Formats an object to produce a string.
`abstract StringBuffer` | `format(Object obj, StringBuffer toAppendTo, FieldPosition pos)` Formats an object and appends the resulting text to a given string buffer.
`AttributedCharacterIterator` | `formatToCharacterIterator(Object obj)` Formats an Object producing an `AttributedCharacterIterator`.
`Object` | `parseObject(String source)` Parses text from the beginning of the given string to produce an object.
`abstract Object` | `parseObject(String source, ParsePosition pos)` Parses text from a string to produce an object.
From class `java.lang.Object`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

## Public constructors

### MessageFormat

    public MessageFormat (String pattern)

Constructs a MessageFormat for the default `FORMAT` locale and the specified pattern. Sets the locale and calls applyPattern(pattern).

Parameters
`pattern` | `String`: the pattern for this message format

Throws
`IllegalArgumentException` | if the pattern is invalid

See also:

- `ULocale.Category.FORMAT`

### MessageFormat

    public MessageFormat (String pattern,
                    Locale locale)

Constructs a MessageFormat for the specified locale and pattern. Sets the locale and calls applyPattern(pattern).

Parameters
`pattern` | `String`: the pattern for this message format
`locale` | `Locale`: the locale for this message format

Throws
`IllegalArgumentException` | if the pattern is invalid

### MessageFormat

    public MessageFormat (String pattern,
                    ULocale locale)

Constructs a MessageFormat for the specified locale and pattern. Sets the locale and calls applyPattern(pattern).

Parameters
`pattern` | `String`: the pattern for this message format
`locale` | `ULocale`: the locale for this message format

Throws
`IllegalArgumentException` | if the pattern is invalid

## Public methods

### applyPattern

    public void applyPattern (String pttrn)

Sets the pattern used by this message format. Parses the pattern and caches Format objects for simple argument types. Patterns and their interpretation are specified in the class description.

Parameters
`pttrn` | `String`: the pattern for this message format

Throws
`IllegalArgumentException` | if the pattern is invalid

### applyPattern

    public void applyPattern (String pattern,
                    MessagePattern.ApostropheMode aposMode)

[icu] Sets the ApostropheMode and the pattern used by this message format. Parses the pattern and caches Format objects for simple argument types. Patterns and their interpretation are specified in the class description.

This method is best used only once on a given object to avoid confusion about the mode, and after constructing the object with an empty pattern string to minimize overhead.

Parameters
`pattern` | `String`: the pattern for this message format
`aposMode` | `MessagePattern.ApostropheMode`: the new ApostropheMode

Throws
`IllegalArgumentException` | if the pattern is invalid

See also:

- `MessagePattern.ApostropheMode`

### autoQuoteApostrophe

    public static String autoQuoteApostrophe (String pattern)

[icu] Converts an 'apostrophe-friendly' pattern into a standard pattern. This is obsolete for ICU 4.8 and higher MessageFormat pattern strings. It can still be useful together with `MessageFormat`.

See the class description for more about apostrophes and quoting, and differences between ICU and `MessageFormat`.

`MessageFormat` and ICU 4.6 and earlier MessageFormat treat all ASCII apostrophes as quotes, which is problematic in some languages, e.g. French, where apostrophe is commonly used. This utility assumes that only an unpaired apostrophe immediately before a brace is a true quote. Other unpaired apostrophes are paired, and the resulting standard pattern string is returned.

Note: It is not guaranteed that the returned pattern is indeed a valid pattern. The only effect is to convert between patterns having different quoting semantics.

Note: This method only works on top-level messageText, not messageText nested inside a complexArg.

Parameters
`pattern` | `String`: the 'apostrophe-friendly' pattern to convert

Returns
`String` | the standard equivalent of the original pattern

### clone

    public Object clone ()

Creates and returns a copy of this object.

Returns
`Object` | a clone of this instance.

### equals

    public boolean equals (Object obj)

Indicates whether some other object is "equal to" this one.

The `equals` method implements an equivalence relation on non-null object references:

- It is reflexive: for any non-null reference value `x`, `x.equals(x)` should return `true`.
- It is symmetric: for any non-null reference values `x` and `y`, `x.equals(y)` should return `true` if and only if `y.equals(x)` returns `true`.
- It is transitive: for any non-null reference values `x`, `y`, and `z`, if `x.equals(y)` returns `true` and `y.equals(z)` returns `true`, then `x.equals(z)` should return `true`.
- It is consistent: for any non-null reference values `x` and `y`, multiple invocations of `x.equals(y)` consistently return `true` or consistently return `false`, provided no information used in `equals` comparisons on the objects is modified.
- For any non-null reference value `x`, `x.equals(null)` should return `false`.

The `equals` method for class `Object` implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values `x` and `y`, this method returns `true` if and only if `x` and `y` refer to the same object (`x == y` has the value `true`).

Note that it is generally necessary to override the `hashCode` method whenever this method is overridden, so as to maintain the general contract for the `hashCode` method, which states that equal objects must have equal hash codes.

Parameters
`obj` | `Object`: the reference object with which to compare.

Returns
`boolean` | `true` if this object is the same as the obj argument; `false` otherwise.

### format

    public final StringBuffer format (Object[] arguments,
                    StringBuffer result,
                    FieldPosition pos)

Formats an array of objects and appends the `MessageFormat`'s pattern, with arguments replaced by the formatted objects, to the provided `StringBuffer`.

The text substituted for the individual format elements is derived from the current subformat of the format element and the `arguments` element at the format element's argument index as indicated by the first matching line of the following table. An argument is unavailable if `arguments` is `null` or has fewer than argumentIndex+1 elements. When an argument is unavailable no substitution is performed.

argType or Format | value object | Formatted Text
--- | --- | ---
any | unavailable | `"{" + argNameOrNumber + "}"`
any | `null` | `"null"`
custom Format `!= null` | any | `customFormat.format(argument)`
noneArg, or custom Format `== null` | `instanceof Number` | `NumberFormat.getInstance(getLocale()).format(argument)`
noneArg, or custom Format `== null` | `instanceof Date` | `DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT, getLocale()).format(argument)`
noneArg, or custom Format `== null` | `instanceof String` | `argument`
noneArg, or custom Format `== null` | any | `argument.toString()`
complexArg | any | result of recursive formatting of a selected sub-message

If `pos` is non-null, and refers to `Field.ARGUMENT`, the location of the first formatted string will be returned. This method is only supported when the format does not use named arguments, otherwise an IllegalArgumentException is thrown.

Parameters
`arguments` | `Object`: an array of objects to be formatted and substituted.
`result` | `StringBuffer`: where text is appended.
`pos` | `FieldPosition`: On input: an alignment field, if desired. On output: the offsets of the alignment field.

Returns
`StringBuffer` |

Throws
`IllegalArgumentException` | if a value in the `arguments` array is not of the type expected by the corresponding argument or custom Format object.
`IllegalArgumentException` | if this format uses named arguments

### format

    public static String format (String pattern,
                    Map<String, Object> arguments)

Creates a MessageFormat with the given pattern and uses it to format the given arguments. The pattern must identifyarguments by name instead of by number.

Parameters
`pattern` | `String`
`arguments` | `Map`

Returns
`String` |

Throws
`IllegalArgumentException` | if the pattern is invalid
`IllegalArgumentException` | if a value in the `arguments` array is not of the type expected by the corresponding argument or custom Format object.

See also:

- `format(Map, StringBuffer, FieldPosition)`
- `format(String, Object[])`

### format

    public final StringBuffer format (Object arguments,
                    StringBuffer result,
                    FieldPosition pos)

Formats a map or array of objects and appends the `MessageFormat`'s pattern, with format elements replaced by the formatted objects, to the provided `StringBuffer`. This is equivalent to either of

> ``format`((Object[]) arguments, result, pos)` ``format`((Map) arguments, result, pos)`

A map must be provided if this format uses named arguments, otherwise an IllegalArgumentException will be thrown.

Parameters
`arguments` | `Object`: a map or array of objects to be formatted
`result` | `StringBuffer`: where text is appended
`pos` | `FieldPosition`: On input: an alignment field, if desired On output: the offsets of the alignment field

Returns
`StringBuffer` | the string buffer passed in as `toAppendTo`, with formatted text appended

Throws
`IllegalArgumentException` | if an argument in `arguments` is not of the type expected by the format element(s) that use it
`IllegalArgumentException` | if `arguments` is an array of Object and this format uses named arguments

### format

    public final StringBuffer format (Map<String, Object> arguments,
                    StringBuffer result,
                    FieldPosition pos)

Formats a map of objects and appends the `MessageFormat`'s pattern, with arguments replaced by the formatted objects, to the provided `StringBuffer`.

The text substituted for the individual format elements is derived from the current subformat of the format element and the `arguments` value corresopnding to the format element's argument name.

A numbered pattern argument is matched with a map key that contains that number as an ASCII-decimal-digit string (without leading zero).

An argument is unavailable if `arguments` is `null` or does not have a value corresponding to an argument name in the pattern. When an argument is unavailable no substitution is performed.

Parameters
`arguments` | `Map`: a map of objects to be formatted and substituted.
`result` | `StringBuffer`: where text is appended.
`pos` | `FieldPosition`: On input: an alignment field, if desired. On output: the offsets of the alignment field.

Returns
`StringBuffer` | the passed-in StringBuffer

Throws
`IllegalArgumentException` | if a value in the `arguments` array is not of the type expected by the corresponding argument or custom Format object.

### format

    public static String format (String pattern,
                    Object... arguments)

Creates a MessageFormat with the given pattern and uses it to format the given arguments. This is equivalent to

> `(new `MessageFormat`(pattern)).`format`(arguments, new StringBuffer(), null).toString()`

Parameters
`pattern` | `String`
`arguments` | `Object`

Returns
`String` |

Throws
`IllegalArgumentException` | if the pattern is invalid
`IllegalArgumentException` | if a value in the `arguments` array is not of the type expected by the corresponding argument or custom Format object.
`IllegalArgumentException` | if this format uses named arguments

### formatToCharacterIterator

    public AttributedCharacterIterator formatToCharacterIterator (Object arguments)

Formats an array of objects and inserts them into the `MessageFormat`'s pattern, producing an `AttributedCharacterIterator`. You can use the returned `AttributedCharacterIterator` to build the resulting String, as well as to determine information about the resulting String.

The text of the returned `AttributedCharacterIterator` is the same that would be returned by

> ``format`(arguments, new StringBuffer(), null).toString()`

In addition, the `AttributedCharacterIterator` contains at least attributes indicating where text was generated from an argument in the `arguments` array. The keys of these attributes are of type `MessageFormat.Field`, their values are `Integer` objects indicating the index in the `arguments` array of the argument from which the text was generated.

The attributes/value from the underlying `Format` instances that `MessageFormat` uses will also be placed in the resulting `AttributedCharacterIterator`. This allows you to not only find where an argument is placed in the resulting String, but also which fields it contains in turn.

Parameters
`arguments` | `Object`: an array of objects to be formatted and substituted.

Returns
`AttributedCharacterIterator` | AttributedCharacterIterator describing the formatted value.

Throws
`NullPointerException` | if `arguments` is null.
`IllegalArgumentException` | if a value in the `arguments` array is not of the type expected by the corresponding argument or custom Format object.

### getApostropheMode

    public MessagePattern.ApostropheMode getApostropheMode ()

[icu]

Returns
`MessagePattern.ApostropheMode` | this instance's ApostropheMode.

### getArgumentNames

    public Set<String> getArgumentNames ()

[icu] Returns the top-level argument names. For more details, see `setFormatByArgumentName(java.lang.String, java.text.Format)`.

Returns
`Set<String>` | a Set of argument names

### getFormatByArgumentName

    public Format getFormatByArgumentName (String argumentName)

[icu] Returns the first top-level format associated with the given argument name. For more details, see `setFormatByArgumentName(java.lang.String, java.text.Format)`.

Parameters
`argumentName` | `String`: The name of the desired argument.

Returns
`Format` | the Format associated with the name, or null if there isn't one.

### getFormats

    public Format[] getFormats ()

Returns the Format objects used for the format elements in the previously set pattern string. The order of formats in the returned array corresponds to the order of format elements in the pattern string.

Since the order of format elements in a pattern string often changes during localization, it's generally better to use the `getFormatsByArgumentIndex()` method, which assumes an order of formats corresponding to the order of elements in the `arguments` array passed to the `format` methods or the result array returned by the `parse` methods. This method is only supported when exclusively numbers are used for argument names. Otherwise an IllegalArgumentException is thrown.

Returns
`Format[]` | the formats used for the format elements in the pattern

Throws
`IllegalArgumentException` | if this format uses named arguments

### getFormatsByArgumentIndex

    public Format[] getFormatsByArgumentIndex ()

Returns the Format objects used for the values passed into `format` methods or returned from `parse` methods. The indices of elements in the returned array correspond to the argument indices used in the previously set pattern string. The order of formats in the returned array thus corresponds to the order of elements in the `arguments` array passed to the `format` methods or the result array returned by the `parse` methods.

If an argument index is used for more than one format element in the pattern string, then the format used for the last such format element is returned in the array. If an argument index is not used for any format element in the pattern string, then null is returned in the array. This method is only supported when exclusively numbers are used for argument names. Otherwise an IllegalArgumentException is thrown.

Returns
`Format[]` | the formats used for the arguments within the pattern

Throws
`IllegalArgumentException` | if this format uses named arguments

### getLocale

    public Locale getLocale ()

Returns the locale that's used when creating or comparing subformats.

Returns
`Locale` | the locale used when creating or comparing subformats

### getULocale

    public ULocale getULocale ()

[icu] Returns the locale that's used when creating argument Format objects.

Returns
`ULocale` | the locale used when creating or comparing subformats

### hashCode

    public int hashCode ()

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by `HashMap`.

The general contract of `hashCode` is:

- Whenever it is invoked on the same object more than once during an execution of a Java application, the `hashCode` method must consistently return the same integer, provided no information used in `equals` comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
- If two objects are equal according to the `equals(Object)` method, then calling the `hashCode` method on each of the two objects must produce the same integer result.
- It is not required that if two objects are unequal according to the `equals(java.lang.Object)` method, then calling the `hashCode` method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

As much as is reasonably practical, the hashCode method defined by class `Object` does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the Java™ programming language.)

Returns
`int` | a hash code value for this object.

### parse

    public Object[] parse (String source)

Parses text from the beginning of the given string to produce an object array. The method may not use the entire text of the given string.

See the `parse(java.lang.String, java.text.ParsePosition)` method for more information on message parsing.

Parameters
`source` | `String`: A `String` whose beginning should be parsed.

Returns
`Object[]` | An `Object` array parsed from the string.

Throws
`ParseException` | if the beginning of the specified string cannot be parsed.
`IllegalArgumentException` | if this format uses named arguments

### parse

    public Object[] parse (String source,
                    ParsePosition pos)

Parses the string.

Caveats: The parse may fail in a number of circumstances. For example:

- If one of the arguments does not occur in the pattern.
- If the format of an argument loses information, such as with a choice format where a large number formats to "many".
- Does not yet handle recursion (where the substituted strings contain {n} references.)
- Will not always find a match (or the correct match) if some part of the parse is ambiguous. For example, if the pattern "{1},{2}" is used with the string arguments {"a,b", "c"}, it will format as "a,b,c". When the result is parsed, it will return {"a", "b,c"}.
- If a single argument is parsed more than once in the string, then the later parse wins.

When the parse fails, use ParsePosition.getErrorIndex() to find out where in the string did the parsing failed. The returned error index is the starting offset of the sub-patterns that the string is comparing with. For example, if the parsing string "AAA {0} BBB" is comparing against the pattern "AAD {0} BBB", the error index is 0. When an error occurs, the call to this method will return null. If the source is null, return an empty array.

Parameters
`source` | `String`
`pos` | `ParsePosition`

Returns
`Object[]` |

Throws
`IllegalArgumentException` | if this format uses named arguments

### parseObject

    public Object parseObject (String source,
                    ParsePosition pos)

Parses text from a string to produce an object array or Map.

The method attempts to parse text starting at the index given by `pos`. If parsing succeeds, then the index of `pos` is updated to the index after the last character used (parsing does not necessarily use all characters up to the end of the string), and the parsed object array is returned. The updated `pos` can be used to indicate the starting point for the next call to this method. If an error occurs, then the index of `pos` is not changed, the error index of `pos` is set to the index of the character where the error occurred, and null is returned.

See the `parse(java.lang.String, java.text.ParsePosition)` method for more information on message parsing.

Parameters
`source` | `String`: A `String`, part of which should be parsed.
`pos` | `ParsePosition`: A `ParsePosition` object with index and error index information as described above.

Returns
`Object` | An `Object` parsed from the string, either an array of Object, or a Map, depending on whether named arguments are used. This can be queried using `usesNamedArguments`. In case of error, returns null.

Throws
`NullPointerException` | if `pos` is null.

### parseToMap

    public Map<String, Object> parseToMap (String source)

[icu] Parses text from the beginning of the given string to produce a map from argument to values. The method may not use the entire text of the given string.

See the `parse(java.lang.String, java.text.ParsePosition)` method for more information on message parsing.

Parameters
`source` | `String`: A `String` whose beginning should be parsed.

Returns
`Map<String, Object>` | A `Map` parsed from the string.

Throws
`ParseException` | if the beginning of the specified string cannot be parsed.

See also:

- `parseToMap(String, ParsePosition)`

### parseToMap

    public Map<String, Object> parseToMap (String source,
                    ParsePosition pos)

[icu] Parses the string, returning the results in a Map. This is similar to the version that returns an array of Object. This supports both named and numbered arguments-- if numbered, the keys in the map are the corresponding ASCII-decimal-digit strings (e.g. "0", "1", "2"...).

Parameters
`source` | `String`: the text to parse
`pos` | `ParsePosition`: the position at which to start parsing. on return, contains the result of the parse.

Returns
`Map<String, Object>` | a Map containing key/value pairs for each parsed argument.

### setFormat

    public void setFormat (int formatElementIndex,
                    Format newFormat)

Sets the Format object to use for the format element with the given format element index within the previously set pattern string. The format element index is the zero-based number of the format element counting from the start of the pattern string.

Since the order of format elements in a pattern string often changes during localization, it is generally better to use the `setFormatByArgumentIndex` method, which accesses format elements based on the argument index they specify.

Parameters
`formatElementIndex` | `int`: the index of a format element within the pattern
`newFormat` | `Format`: the format to use for the specified format element

Throws
`ArrayIndexOutOfBoundsException` | if formatElementIndex is equal to or larger than the number of format elements in the pattern string

### setFormatByArgumentIndex

    public void setFormatByArgumentIndex (int argumentIndex,
                    Format newFormat)

Sets the Format object to use for the format elements within the previously set pattern string that use the given argument index. The argument index is part of the format element definition and represents an index into the `arguments` array passed to the `format` methods or the result array returned by the `parse` methods.

If the argument index is used for more than one format element in the pattern string, then the new format is used for all such format elements. If the argument index is not used for any format element in the pattern string, then the new format is ignored. This method is only supported when exclusively numbers are used for argument names. Otherwise an IllegalArgumentException is thrown.

Parameters
`argumentIndex` | `int`: the argument index for which to use the new format
`newFormat` | `Format`: the new format to use

Throws
`IllegalArgumentException` | if this format uses named arguments

### setFormatByArgumentName

    public void setFormatByArgumentName (String argumentName,
                    Format newFormat)

[icu] Sets the Format object to use for the format elements within the previously set pattern string that use the given argument name.

If the argument name is used for more than one format element in the pattern string, then the new format is used for all such format elements. If the argument name is not used for any format element in the pattern string, then the new format is ignored.

This API may be used on formats that do not use named arguments. In this case `argumentName` should be a String that names an argument index, e.g. "0", "1", "2"... etc. If it does not name a valid index, the format will be ignored. No error is thrown.

Parameters
`argumentName` | `String`: the name of the argument to change
`newFormat` | `Format`: the new format to use

### setFormats

    public void setFormats (Format[] newFormats)

Sets the Format objects to use for the format elements in the previously set pattern string. The order of formats in `newFormats` corresponds to the order of format elements in the pattern string.

If more formats are provided than needed by the pattern string, the remaining ones are ignored. If fewer formats are provided than needed, then only the first `newFormats.length` formats are replaced.

Since the order of format elements in a pattern string often changes during localization, it is generally better to use the `setFormatsByArgumentIndex` method, which assumes an order of formats corresponding to the order of elements in the `arguments` array passed to the `format` methods or the result array returned by the `parse` methods.

Parameters
`newFormats` | `Format`: the new formats to use

Throws
`NullPointerException` | if `newFormats` is null

### setFormatsByArgumentIndex

    public void setFormatsByArgumentIndex (Format[] newFormats)

Sets the Format objects to use for the values passed into `format` methods or returned from `parse` methods. The indices of elements in `newFormats` correspond to the argument indices used in the previously set pattern string. The order of formats in `newFormats` thus corresponds to the order of elements in the `arguments` array passed to the `format` methods or the result array returned by the `parse` methods.

If an argument index is used for more than one format element in the pattern string, then the corresponding new format is used for all such format elements. If an argument index is not used for any format element in the pattern string, then the corresponding new format is ignored. If fewer formats are provided than needed, then only the formats for argument indices less than `newFormats.length` are replaced. This method is only supported if the format does not use named arguments, otherwise an IllegalArgumentException is thrown.

Parameters
`newFormats` | `Format`: the new formats to use

Throws
`NullPointerException` | if `newFormats` is null
`IllegalArgumentException` | if this formatter uses named arguments

### setFormatsByArgumentName

    public void setFormatsByArgumentName (Map<String, Format> newFormats)

[icu] Sets the Format objects to use for the values passed into `format` methods or returned from `parse` methods. The keys in `newFormats` are the argument names in the previously set pattern string, and the values are the formats.

Only argument names from the pattern string are considered. Extra keys in `newFormats` that do not correspond to an argument name are ignored. Similarly, if there is no format in newFormats for an argument name, the formatter for that argument remains unchanged.

This may be called on formats that do not use named arguments. In this case the map will be queried for key Strings that represent argument indices, e.g. "0", "1", "2" etc.

Parameters
`newFormats` | `Map`: a map from String to Format providing new formats for named arguments.

### setLocale

    public void setLocale (ULocale locale)

Sets the locale to be used for creating argument Format objects. This affects subsequent calls to the `applyPattern` method as well as to the `format` and `formatToCharacterIterator` methods.

Parameters
`locale` | `ULocale`: the locale to be used when creating or comparing subformats

### setLocale

    public void setLocale (Locale locale)

Sets the locale to be used for creating argument Format objects. This affects subsequent calls to the `applyPattern` method as well as to the `format` and `formatToCharacterIterator` methods.

Parameters
`locale` | `Locale`: the locale to be used when creating or comparing subformats

### toPattern

    public String toPattern ()

Returns the applied pattern string.

Returns
`String` | the pattern string

Throws
`IllegalStateException` | after custom Format objects have been set via setFormat() or similar APIs

### usesNamedArguments

    public boolean usesNamedArguments ()

[icu] Returns true if this MessageFormat uses named arguments, and false otherwise. See class description.

Returns
`boolean` | true if named arguments are used.

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